Pivoted tower single point mooring systems

ABSTRACT

A PIVOTED TOWER SINGLE POINT MOORING AND CARGO HANDLING SYSTEM, PRIMARILY FOR TANKER VESSELS, IS PROVIDED WHICH COMPRISES A BUOYANCY CHAMBER WITH ATTACHED RIGID PIPE WHICH IS PIVOTALLY CONNECTED TO A MOORING FOUNDATION, A FLEXIBLE CARGO CONDUIT FOR CONDUCTING CARGO FROM THE BASE OF THE BUOYANCY CHAMBER TO THE VESSEL, MEANS FOR CONDUCTING CARGO FROM THE FOUNDATION THROUGH THE PIPE TO THE BASE OF THE BUOYANCY CHAMBER AND SWIVELING   MEANS AT THE BASE OF THE BUOYANCY CHAMBER FOR PERMITTING THE FLEXIBLE CARGO CONDUIT TO ROTATE WITH RESPECT TO THE BUOYANCY CHAMBER.

Oct. 26, 1971 J. F. FLORY ETA 3,614,869

PIVOTED TOWER SINGLE POINT MOORING SYSTEMS Filed Sept. 9. 1969 2Shoots-Sheet 1 ni'lllar John E Flory William R. Phi/fiber 'NVENTORS BYf/ ATTORNEY Oct. 26, 1971 FQFLORY ETAL PIVOTED TowfiR SINGLE POINTMOORING SYSTEMS i1 Sheets-Sheet 7'! Filed Sept. 9, 1969 Fig. 2

John F. Flory William R. Phi/fiber INVENTORS ATTORNEY BY W 3,614,869PIVOTED TOWER SINGLE POINT MOORING SYSTEMS John F. Flory, Morristown,NJ., and William R. Phillrber,

Sale, Victoria, Australia, assignors to Esso Research and EngineeringCompany Filed Sept. 9, 1969, Ser. No. 856,446 Int. Cl. E02b 17/02; B63b21/00 U.S. Cl. 61-46 7 Claims ABSTRACT OF THE DISCLOSURE A pivoted towersingle point mooring and cargo handling system, primarily for tankervessels, is provided which comprises a buoyancy chamber with attachedrigid pipe which is pivotally connected to a mooring foundation, aflexible cargo conduit for conducting cargo from the base of thebuoyancy chamber to the vessel, means for conducting cargo from thefoundation through the pipe to the base of the buoyancy chamber andswiveling means at the base of the buoyancy chamber for permitting theflexible cargo conduit to rotate with respect to the buoyancy chamber.

FIELD OF THE INVENTION This invention relates to a single point mooringsystem for sea going ships, particularly tanker vessels, wherein fluidcargo handling facilities are integrated with the mooring system. Moreparticularly, this invention relates to an integrated mooring and cargohandling facility comprising a buoyancy chamber and anchor leg whereinthe anchor leg is a rigid pipe capable of supporting the mooring loadand of conducting fluid cargo to a fluid swivel rotatably mounted at thebase of the buoyancy chamber.

PRIOR ART With the advent of exceptionally large tanker ships, i.e.,200,000 d.w.t. and up, the loading and unloading of such ships hasbecome increasingly complex. These ships generally have such deep draftsthat natural harbors often cannot accommodates them, and their size issuch that mooring forces are quite high. Rather than create new harborsat an exceedingly high cost, it has been suggested to moor such ships indeep water and to transfer the fluid cargo via underwater pipelines toshore based facilities.

When a ship is moored to a single buoy in such a manner that it is freeto swing around the buoy, the system is referred to as single pointmooring. The ship is usually moored to the buoy by bow hawsers and isfree to rotate 360 about the buoy, thereby reducing mooring forces.Provisions must be made to transfer the fluid cargo between the ship andthe underwater pipeline as the ship rotates. Previous single pointmooring systems have been designed which have a multiplicity of anchorchains and underwater fluid conduits, and which require means forpreventing fouling of the one with the other. Other prior art singlepoint mooring systems have been designed which have massive turntablesmounted on the deck of a buoy or tower to enable the tanker to swingaround the mooring point. By the practice of this invention, however, anintegrated single point mooring and cargo handling facility is providedwhereby the anchor leg of the mooring system simultaneously serves asthe underwater fluid conduit. Additionally, the fluid conduit isconnected Patented Oct. 26, 1971 to a swivel positioned beneath thebuoyancy chamber where it is protected from the severe environment atthe sea surface.

SUMMARY OF THE INVENTION In accordance with this invention, a pivotedtower single point mooring system having integrated cargo handlingfacilities is provided wherein a buoyancy chamber, located at or nearthe surface of the sea, is anchored to a foundation fixed to the seabottom through a single anchor leg of predetermined length which holdsthe buoyancy chamber down against its natural buoyancy force. The anchorleg comprises a rigid conduit or pipe which is capable of conductingcargo, and is capable of carrying a mooring load, means for pivotallyconnecting the lower end of the rigid pipe to the mooring foundation,and optional means for pivotally connecting the buoyancy chamber to theupper end of the rigid pipe, each of the pivotally connecting meanshaving internal fluid passages. A fluid swivel means surrounds the baseof the buoyancy chamber and a flexible fluid conduit communicatesbetween the fluid swivel means and the vessel thus comprising a cargotransfer path between the foundation and the vessel. Additionally, anelastic mooring line is connected through a load carrying swivel to thetop of the buoyancy chamber and extends to the bow of the vessel, thusmooring the vessel while permitting it to rotate around the mooringsystem.

Since the flexible conduit between the vessel and the system isconnected underwater, i.e., at the base of the buoy, several distinctadvantages are obtained. Previous designs for single point mooringsystems have utilized expensive floating loading hoses connected to thetop of the buoy through turntable or swivel arrangements on the buoy.Such designs are objectionable in that hose connections near the surfaceof the sea are subjected to the full force of the waves and are apt totangle with mooring lines. Furthermore, the splash zone environment atthe surface of the sea, is especially severe on mechanical componentsdue to the alternate salt water immersion and drying to which suchcomponents are subjected. The practice of this invention eliminatesthese problems.

DRAWING DESCRIPTION This invention, in several of its embodiments, willbe more easily understood by referring to the attached drawings whereidentical numerals depict identical components.

FIG. 1 shows a mooring tower comprising a buoyant chamber, an underwaterpipe, a foundation, a ball socket joint and a fluid swivel meanssurrounding the base of the buoyant chamber.

FIG. 2 shows an alternate embodiment wherein spherical elastomer jointsare utilized at the connection between the buoyant chamber and the pipeand at the con nection between the pipe and the foundation.

FIG. 3 is a detail of the fluid swivel means and the spherical elastomerjoint at the base of the buoyant chamber.

FIG. 4 is a detail of the ball socket joint at the base of the pipe.

Referring now to FIG. 1, mooring foundation 20 is anchored to the seabottom, e.g., by piles, etc., and receives an underwater pipe 18 fromshore based facilities. Buoyancy chamber 32 is located at the seasurface and contains a mooring eye 34 connected to a mooring swivelcapable of receiving bow hawsers 36 from a ship, not shown. Disposedbetween buoyancy chamber 32 and foundation 20 is a rigid pipe 24 capableof supporting a mooring load and of predetermined length such that thebuoyancy chamber is generally at or near the surface of the sea.

The pipe 24 is connected to the foundation 20 by a ball socket joint 22having an internal fluid passage. The ball socket joint, shown in detailin FIG. 4, allows pipe 24 to pivot about axes in the horizontal planebut resists any rotational movement of pipe 24 about a vertical axismuch like a universal joint. The ball socket joint is similar (butlarger in size) to those ball socket joints now readily available toindustry. Essentially, and referring to FIG. 4, the joint consists of aspherical socket 51 into which a cylinder 52 having a ball shaped end 53is secured. Keys 54 provided on the ball project into keyways 55 in thesocket 51 to prevent rotation about a vertical axis. The outer diameterof the ball and the inner diameter of the socket are arranged in sealingrelationship by sealing glands 56 and 57. The underwater pipe 18communicates with pipe 24 through the passage 58 in ball joint 22 by wayof foundation piping shown in dotted lines. By virtue of this pivotconnection, the buoyancy chamber 32 and pipe 24 may be pulled off thevertical line through the center of the foundation by the movement ofthe ship (due to wind, waves, and/or current) such that the buoy may, atcertain times, be partially submerged.

At the base of buoyancy chamber 32, a fluid swivel assembly 26 with aninternal load carry member is mounted. This fluid swivel assembly isshown in greater detail in FIG. 3 and will be described later. Pipe yoke28 is attached through fluid swivels 29 to outlets of the fluid swivelassembly 26 and is joined to loading hose 30, which transfers cargobetween the vessel and the mooring tower. The fluid swivel joints andhose connections are then below the water surface and protected from thewave and splash zone environments. The hose 30 is generally a floatinghose which rises to the surface some distance from the mooring tower. Asthe vessel swings around the buoyancy chamber 32, i.e. due to the actionof wind, waves and/or current, the hose 30 will cause the fluid swivelassembly 26 to rotate with respect to pipe 24 and buoyancy chamber 32.

FIG. 2 shows an alternate embodiment wherein elastomeric bearings areutilized. Pipe 24 is connected to foundation 20 through one or moreelastomeric bearings 38 in place of the ball socket joint. One or moreelastomeric bearings 37 are placed at the junction between the buoyancytank 32 and the pipe 24. The use of the elastomeric bearings acts as aflexible joint at this point and greatly reduces bending moments on thepipe 24.

FIG. 3 shows a detail cross section through the base of the buoyancychamber, the fluid swivel assembly, the elastomeric bearing and the topof the pipe in the system of FIG. 2. A rigid cross shaped load carryingmember 40 is disposed between pipe 24 and buoyancy chamber 32 and may beconsidered as forming part of the base of the buoyancy chamber 32 and issecurely mounted to the top of pipe 24. Thus, the pipe 24 and buoyancychamber 32 will pivot about the foundation 20 as a single unit. The loadcarrying member is designed to take both axial and lateral loads andbending moments due to mooring loads applied to the buoyancy chamber. Ahousing 41 is rotatably mounted around the load carrying member 40 onsealed bearings 43 and 45. Fluid pas sages 27 in the load carryingmember 40 communicate with port 46 in the side of the housing 41. Thus,as the loading hose (connected via port 46 to housing 41) moves with themovement of the vessel, housing 41 will rotate about load carryingmember 40. This fluid swivel assembly is described in greater detail incopending appli- 4 cation Ser. No. 856,259, filed Sept. 9, 1969,assigned to the same assignee as that of the present application.

Hose connection flange 42 is coupled with port 38 by elastomeric bearing39. The elastomeric bearing 39 provides flexibility at the hoseconnection point thus relieving stress in the floating loading hose.Load carrying member 40 is connected with the top of the pipe 24 byelastomeric bearing 37. The elastomeric bearing 37 provides flexibilityat the junction between the buoyancy chamber 32 and the pipe 24 thusreducing greatly the moment loads in the pipe and load bearing member.The elastomer bearing 37 could alternately be located between loadcarrying member 40 and buoyancy chamber 32 or elastomeric bearings couldbe provided both above and below the load carrying member.

The elastomeric bearings are constructed of alternate hemisphericallayers of elastomer, e.g., silicone rubbers, neoprene, or other waterresistant rubber, and metal, e.g. steel. The elastomeric layers areeither molded or secondarily bonded to the metal spacers to provide anintegral structure. When the bearing is deflected to the side theelastomeric material deforms in shear. The joint does not rotate aboutits axis under torsional load but does bend under moment loads much as auniversal joint. A cavity is provided in the joint through which fluidmay be conveyed and the joint can Withstand relatively high internal andexternal pressures. Such joints are sold under the trade name Locksealby the Lockheed Propulsion Co.

Having now described the invention, various modifications of which willbe obvious to those skilled in the art, the following claims are made.

What is claimed is:

1. A single point mooring and cargo handling system for tanker vesselswhich comprises, in combination:

a mooring foundation anchored to the sea bottom,

a buoyancy chamber located at or near the surface of the sea,

a rigid pipe, capable of supporting a mooring load and of conductingcargo, disposed between said foundation and said buoyancy chamber,

pivot means connecting said pipe to said foundation and containing afluid passage in communication with said pipe,

conduit means for conducting fluid between said vessel and said system,and

fluid swivel means disposed between said pipe and said buoyancy chamberand rotatably mounted around the base of said buoyancy chamber, saidfluid swivel means being capable of rotating with respect to saidbuoyancy chamber and being in fluid communication with said pipe andsaid conduit means.

2. The system of claim 1 wherein flexible pivoting means are providedbetween said buoyancy chamber and said pipe, said flexible pivot meanscontaining a fluid passage in communication with said pipe.

3. The system of claim 1 wherein flexible pivoting means are providedbetween said conduit means and said pipe, said flexible pivot meanscontaining a fluid passage in communication with said pipe and saidconduit means.

4. The system of claim 1 wherein flexible pivot means are providedbetween said buoyancy chamber and said fluid swivel means.

5. The system of claim 1 wherein said pivot means connecting said pipeand said foundation is a ball socket joint having an internal fluidpassage.

6. The system of claim 1 wherein said pivot means connecting said pipeand said foundation is a flexible spherical bearing comprisingalternating layers of elastomeric and metallic materials and having aninternal fluid passage.

7. The system of claim 1 wherein undersea conduits are provided forconducting fluid to and from said foundation and means are provided forfluid communication between said undersea conduits and said fluidpassage contained in said pivot means.

References Cited UNITED STATES PATENTS Ault 61-46 X Ault 6146 X Foster61-465 X Koonce et a1. 61--46.5

9/1969 Schirtzinger 1- l14230 X 1l/1969 Manning 1- 98 P OTHER REFERENCES5 World Oil, Vil ain et 211., Feb. 1, 1968, pp. 38, 39.

J. KARL BELL, Primary Examiner US. Cl. XR.

